The present invention relates to the field of optical switching in general and, more particularly, to optical switching nodes for use in an optical network. The invention also pertains to protocols governing the behaviour of the switching nodes.
The development of high-capacity networks has been driven by the need to establish high-bandwidth data connections among remote sites, for instance, between clients and servers. Most often, the communications infrastructure for such a network is provided by one or more long-distance carriers serving the geographic region that encompasses the various remote sites. A carrier may lease fiber optic lines to customers wishing to establish high-capacity connections. Within the carrier""s network, optical switching nodes are then configured to support the desired connections.
Usually, a carrier leases its fiber optic lines with a view to long-term usage thereof. Thus, switch configurations established at the time of provisioning the high-capacity connections are expected to remain in place for a period of months or years. Therefore, the switches in the network can be configured manually with virtually no impact on cost or quality of service provided.
However, it is not feasible to manually configure a large number of switches when dealing with a network whose size and/or topology are in constant evolution. Furthermore, the manual configuration of switches cannot accommodate situations in which the bandwidth or quality of service requirements of the traffic to be transported through the network is time-varying or if there is urgency in establishing new high-capacity connections through the network. Although it is desirable to provide switches which are automatically reconfigurable as a function of changes to the topology and traffic load of the network, such a capability is currently not available.
Moreover, the most common approach to establishing end-to-end data connections in current optical networks relies on the utilization of the same wavelength, say xcexx, along a manually configured path throughout the network. This prevents the establishment of other data connections using xcexx as an end-to-end wavelength if part of the path corresponding to the new connection intersects part of the path corresponding to the original connection. This places a severe constraint on wavelength usage in a current optical network, with the effect of drastically reducing the overall bandwidth efficiency in the network.
Thus, it is apparent that there is a need in the industry to provide an optical switching node which overcomes the above stated disadvantages.
The invention can be described broadly as a switching node that includes an optical switch fabric, a wavelength conversion unit and a control unit. The optical switch fabric is connected to the control unit and is used for switching optical signals arriving on a set of input optical fiber segments over to a set of output optical fiber segments in accordance with mapping instructions received from the control unit. The wavelength conversion unit is connected to the optical switch fabric and is used for modifying the wavelengths occupied by incoming or switched optical signals in accordance with conversion commands received from the control unit.
The control unit is used for exchanging control information with other switching nodes using a network layer protocol and generating the mapping instructions and the conversion commands based on this control information. This switching node allows the input and output wavelengths of an optical data signal to occupy different wavelengths, which provides many benefits, among which is included the benefit of increased wavelength efficiency in an optical network.
Preferably, the control information is exchanged using a out-of-band control channel such as an optical supervisory channel.
Preferably, the control unit includes a processor and a memory element accessible by the processor. The memory element preferably stores a routing table and a wavelength availability table. The routing table contains a next hop switching node field associated with every possible pair of terminal switching nodes. The wavelength availability table contains the identity of the switching nodes connected to any of the ports by a respective multi-wavelength fiber optic link and, for each wavelength, an indication of whether that wavelength is occupied or available.
The switching node is most often connected to a previous switching node in a path identified by a first terminal switching node and a second terminal switching node. In such a scenario, the control unit is preferably operable to receive messages from the previous switching node.
If the message is a so-called CONNECTION_REQUEST message, then the control unit will preferably access the wavelength availability table to identify an available wavelength on the link between the current and previous switching nodes, the available wavelength being associated with one of the input optical fiber segments.
If the current switching node is the second terminal switching node, then the control unit will preferably generate mapping commands for establishing a connection, using the available wavelength, between the input optical fiber segment associated with the available wavelength and one of the output optical fiber segments; and send a CONNECTION_CONFIRM message to the previous switching node.
Otherwise, if the current switching node is not the second terminal switching node, the control unit will preferably access the routing table to determine the contents of the next hop switching node field associated with the first and second terminal switching nodes; and forward the CONNECTION_REQUEST message to the switching node identified by the next hop switching node field.
If, on the other hand, the message is a so-called CONNECTION_CONFIRM message, then the control unit will preferably generate mapping commands for establishing a connection using the available wavelength between the input optical fiber segment associated with the available wavelength and one of the output optical fiber segments; and send a CONNECTION_CONFIRM message to the previous switching node.
In order to accommodate a packet-based architecture, in which incoming optical signals are formed of packets having a header and a payload, the switching node may include an additional conversion unit connected to the input optical fiber segments and to the control unit, for extracting the header of each packet. In this case, the mapping instructions and the conversion commands generated by the controller will further be dependent on the information contained in the header of each packet.
In another embodiment, the switching node includes a first set of optoelectronic converters and a second set of optoelectronic converters. The first set of converters is used for converting input optical signals occupying respective wavelengths into electronic signals, while the second set of converters is used for converting output electronic signals into output optical signals occupying respective wavelengths.
The switching node also includes a digital switch fabric connected to the optoelectronic converters, for switching the input electronic signals over to the output electronic signals in accordance with switching instructions. Finally, the switching node includes a control unit connected to the digital switch fabric and to the optoelectronic converters. The control unit exchanges control information with other switching nodes using a network layer protocol and generates the switching instructions based on the control information.
In this embodiment, the switching node provides grooming functionality in the sense that the input electronic signals can be reformatted so that when these reformatted signals are switched and then converted into an optical format by the second set of converters, the resulting optical signal can be in a desired format. This improves compatibility among end user equipment in a network.
The invention may be summarized at the network level as a method of establishing a data connection between first and second terminal switching nodes. The network is understood to include the terminal switching nodes as well as a group of other switching nodes interconnected by multi-wavelength optical links.
The method includes a first step of identifying a path comprising a set of links and wavelengths for transporting data between the first and second terminal switching nodes via zero or more intermediate switching nodes.
The method also includes the step of, at each intermediate switching node connected to a respective ingress link and a respective egress link in the identified path, switching the optical signals arriving on the respective ingress link over to the respective egress link and performing wavelength conversion if the wavelengths occupied on the respective ingress and egress links are different. Advantageously, this allows a data connection to be established using different wavelengths along the way.
The invention can also be summarized as a wavelength distribution protocol for enabling a data connection to be established between a first terminal switching node and a second terminal switching node via zero or more intermediate switching nodes along a path in a network. The protocol is executed at the various switching nodes in the network.
At each current switching node connected in the path between a previous switching node and/or a next switching node by respective optical links, the protocol includes the capability to receive messages from the previous or next switching node.
If the message is a CONNECTION_REQUEST message, then if the current switching node is not the first terminal switching node, the protocol includes identifying and storing an available wavelength on the link between the current and previous switching nodes.
Also, if the message is a CONNECTION_REQUEST message and if the current switching node is indeed the second terminal switching node, the protocol includes establishing a connection using the available wavelength and sending a CONNECTION_CONFIRM message to the previous switching node, otherwise forwarding the CONNECTION_REQUEST message to the next switching node.
If, however, the message is a CONNECTION_CONFIRM message, then the protocol includes establishing a connection using the previously stored available wavelength and if the current switching node is not the first terminal switching node, sending a CONNECTION_CONFIRM message to the previous switching node.
For the protocol to operate as intended, an initial CONNECTION_REQUEST message is assumed to be sent to the first terminal switching node upon initially requesting the data connection.
By participating in this protocol, switching nodes automatically participate in the end-to-end establishment of data connections using dynamically assigned wavelengths, which improves overall bandwidth efficiency of the optical network and provides more flexible protection switching, which no longer requires the input and output wavelengths to be identical.